Disabling buttons one at a time - vb.net

Question

My partner and I are trying to figure out how to disable a button one at a time. We're making a program in Visual Studio Express 2012 that will disable a button once it is typed in a textbox. For example, we have five letters placed seperately on five different buttons If we were to put the letter "D" on the textbox, the button that contains that specific letter will be disabled. We're using the code
If e.KeyCode = Keys.D Then
Button1.Enabled = False
End If
Now that works, BUT if there were two or more buttons that has the same letters, all of them disables because then the code will be :
If e.KeyCode = Keys.D Then
Button1.Enabled = False
End If
If e.KeyCode = Keys.D Then
Button2.Enabled = False
End If
My problem would be in what way could I distinguish those buttons that has the same letter from one another so that when I type the letter on a textbox, only one button disables and when I type it in again, another button containing the same letter disables. Thanks!

Answer 1

Assuming all of the buttons are not in child panels:
If e.KeyCode = Keys.D Then
For Each b As Button In Me.Controls.OfType(Of Button)()
If b.Text.Contains("D") AndAlso b.Enabled Then
b.Enabled = False
Exit For
End If
Next
End If

Answer 2

This will recursively iterate all controls on the form looking for buttons and disable them based on the characters and number of characters entered into the textbox:
Private Sub textBox1_TextChanged(sender As Object, e As System.EventArgs)
Dim text As String = TryCast(sender, TextBox).Text.ToLower()
For Each b As Button In GetAllButtons(Me)
b.Enabled = True
Next
For Each c As Char In text
Dim count As Integer = text.Count(Function(cc) cc = c)
For i As Integer = 0 To count - 1
For Each b As Button In GetAllButtons(Me).Where(Function(x) x.Text.ToLower().Contains(c.ToString())).Take(count).ToList()
b.Enabled = False
Next
Next
Next
End Sub
Private Function GetAllButtons(control As Control) As List(Of Button)
Dim allButtons As New List(Of Button)()
If control.HasChildren Then
For Each c As Control In control.Controls
allButtons.AddRange(GetAllButtons(c))
Next
ElseIf TypeOf control Is Button Then
allButtons.Add(TryCast(control, Button))
End If
Return allButtons
End Function